1. Field of the Invention
The present invention relates to a resin composition, a resin molding and a method for inhibiting polymerization of a vinyl compound, and particularly to a method for inhibiting polymerization in a distillation process using a distillation tower containing packing upon a production of a vinyl compound in order to prevent a polymerizate from producing and to conduct the distillation smoothly and cost-effectively.
2. Description of the Related Art
A vinyl compound is polymerizable compound having a double bond. The polymerization is initiated by a radical induced by light, heat, a peroxide or the like, an ionic substance, a metal complex or the like. A diversity in the polymerization initiation means that undesirable polymerization, i.e., early polymerization is initiated by various triggers. The fact has been a great technical problem upon a production and a preservation of the vinyl compound.
In a method for producing the vinyl compound, distillation using a distillation tower containing packing, which is a normal refining step to obtain a high purity vinyl compound, is a step wherein polymerization is most likely to occur. Specifically, polymerization is most likely to occur at an inside of the distillation tower such as a steam condensing part and a residence part of the condensate. Accordingly, many efforts have been made and many ideas have been introduced.
For example, the following are disclosures concerning methacrylic acid, acrylic acid and esters thereof.
The inside of the distillation tower is occupied with a vapor mainly including the vinyl compound and the condensate thereof. In order to prevent polymerization in the distillation tower, a polymerization inhibitor that vaporizes together with the vinyl compound, i.e., the polymerization inhibitor having a high vapor pressure is preferable. Japanese Patent Application Laid-Open No. Showa 50(1975)-64214, No. Heisei 2(1990)-17151 and No. Heisei 7(1995)-316093 disclose a use of a combination of a polymerization inhibitor having a low vapor pressure for preventing polymerization of a crude liquid and the polymerization inhibitor having a high vapor pressure. The polymerization inhibitors are taken into a product. If an excess amount of polymerization inhibitors are used for fear of the polymerization, then the purity of the product is tend to be lowered or the quality of the product is tend to be deteriorated due to coloring caused by polymerization inhibitors. The excess amount of polymerization inhibitors in the product are also undesirable for producing a polymer using the vinyl compound as a raw material. When the vapor drifts in a short path in the distillation tower containing the packing, the residence part is formed in the distillation tower and the polymerization inhibitors never be introduced into the residence part. Accordingly, providing the polymerization inhibitor having the high vapor pressure is meaningless.
Japanese Examined Patent Publication No. Showa 50(1975)-6449, Japanese Patent Application Laid-Open No. Showa 49(1974)-85016, No. Showa 50(1975)-101313, No. Showa 59(1984)-7147, No. Showa 64(1989)-9957, No. Showa 64(1989)-42443, No. Showa 64(1989)-66140, No. Heisei 2(1990)-248402 and No. Heisei 7(1995)-53449 disclose a method for allowing a gas to exist which has a polymerization inhibiting effect such as oxygen, air, nitrogen oxide or a combination of such gases and a polymerization inhibitor in the distillation tower. Oxygen and air are very effective in view of less contamination of the product and cost efficiency. However, oxygen and air have less polymerization inhibiting effect themselves and are typically used in combination with an other polymerization inhibitor. Nitrogen monoxide may deteriorate the product and the polymerization inhibitor used therewith, and easily react with oxygen in the air into nitrogen dioxide having no polymerization inhibiting effect. Thus, the nitrogen monoxide involves a technical difficulty in handling. According to the method, similar to the former method using the polymerization inhibitor having a high vapor pressure, when the vapor drifts in a short path in the distillation tower containing the packing, the polymerization inhibiting effect for the residence part formed is no more expected.
Japanese Examined Patent Publication No. Showa 50(1975)-6449 and Japanese Patent Application Laid-Open No. Heisei 2(1990)-193944 disclose a method for spraying a polymerization inhibitor dissolved in a vinyl compound from a top of a distillation tower. According to the method, a high polymerization inhibiting effect is expected. However, there is economical problems that an expensive polymerization inhibitor should be provided continuously. In addition, it is required to distribute the polymerization inhibitor every nook and corners of an inside of the distillation tower. However, a dead space where the polymerization inhibitor does not reach is formed and no polymerization inhibiting effect is expected in the dead space.
Japanese Patent Application Laid-Open No. Showa 63(1988)-41514, No. Showa 63(1988)-41440 and No. Heisei 1(1989)-180850 disclose a method for lowering a residence amount of fine condensate of a vinyl compound on a surface of a metal to inhibit an adhesion of a polymer to an inner surface of distilling equipment by a smoothing with an electrolytic polishing, a mechanical polishing, a surface treatment with nitric acid or the like. The method does not inhibit polymerization but avoid polymerization. Therefore, no great advantage is expected.
Other examples of the disclosure include a use of an empty distillation tower without packing, retarded numbers of stages for refining, a use of a thin film distillation tower having a few heat history disclosed in Japanese Patent Application Laid-Open No. Showa 62(1987)-201852 and distillation under high vacuum to decrease temperature. Some of the methods sacrifice for purity of a product to some extent, or urge economical burdens on facility and operation. Accordingly, distillation using a distillation tower containing packing having required numbers of stages is accompanied by a serious risk and therefore has scarcely been utilized especially for the vinyl compound that is highly polymerizable, although such distillation tower is the most common and efficient refining means for obtaining a high purity product.